The invention relates to a circuit for monitoring the faultless state and/or for detecting the faulty state of a system, for example of a cable railway or chairlift system, with a plurality of monitoring and detection devices and with at least one control and evaluation unit, the monitoring and detection devices being series-connected to one another and to the control and evaluation unit and having the potential to be interrogated with respect to their state, especially with respect to their operating state.
Systems of the most varied type, especially so-called safety-relevant systems, often require continuous monitoring, i.e. monitoring of the faultless state, and generally in conjunction with the monitoring of the faultless state, the detection of a faulty state. As soon as a faulty state has been recognized, a safety-relevant measure is initiated.
In cable railway or chairlift systems the location of the cable relative to the cable pulleys which carry or guide the cable must be monitored as the safety-relevant criterion. If the actual position of the cable does not correspond to the nominal position relative to at least one cable pulley, safety-relevant measures must be taken. For a small deviation between the actual location of the cable and its nominal location, the safety-relevant measure derived therefrom can be a reduction of the cable speed. If the deviation between the actual position of the cable and the nominal position exceeds a stipulated boundary value, the safety-relevant measure in any case consists in that the cable railway system or chairlift system is instantly shut down.
In electrical and now of course also electronic circuits which operate as control circuits, it is distinguished between the working current principle and the bias current principle. In the working current principle, control interventions are initiated for example into the system when a large enough control current is flowing in the control circuit. In the control circuit which operates according to the working current principle the existing switching devices are built as make contacts; they are electrically conductive when they are actuated. In contrast, in the bias current principle control interventions are initiated for example into the system when no control current is flowing in the control circuit. In the control circuits which operate according to the bias current principle the existing switching devices are made as break contacts; they are electrically nonconductive when they are actuated.
In the control circuit built according to the working current principle, as detailed above, control interventions are initiated into an assigned system only when a large enough control current is flowing in the control circuit. The prerequisite therefore is that on the one hand the necessary operating voltage is present, that on the other hand there are no breaks in the line, and that ultimately the switching device which is made as a make contact and which is present in this control circuit is serviceable. In contrast, in the control circuit which operates according to the bias current principle control interventions are initiated into the system which belongs thereto when no control current is flowing in the control circuit.
The aforementioned statements on the working current principle and the bias current principle illustrate that control circuits which are designed to trigger safety-relevant measures must work according to the bias current principle. Since the currentless state in the control circuit is evaluated such that the corresponding system is in a safe state, failure of the operating voltage and a break in the line always lead to the system being moved into the safe state if it is not in the safe state. In a cable railway or chairlift system the safe state is of course the cable drive turned off.
In the control circuits which work according to the working current principle, therefore in control circuits in which the switching devices are made as make contacts, the switching devices are connected in parallel; after actuating a switching device built as a make contact the control circuit takes effect overall. Conversely, in the control circuits operating according to the bias current principle, therefore in control circuits in which the switching devices are made as break contacts, the switching devices are connected in series; after actuating a switching device made as a break contact the control circuit becomes currentless and thus operative overall.
So that in a circuit of the type under consideration, when a faulty state of the system has been detected by the series connection of all monitoring and detection devices, the fault can be located, it is provided that the monitoring and detection devices can be interrogated with respect to their state, especially with respect to their operating state.
How the monitoring and detection devices are made individually in a circuit of the described type depends mainly on how the system is built in particular, in which using this circuit the faultless state is to be monitored and the faulty state is to be detected. If the system is a cable railway or chairlift system, it is provided according to the not yet published patent application Ser. No. 196 20 065.2 that each monitoring and detection device has three proximity indicators and the latter are logically interconnected directly or indirectly. Here the problem is the increased amount of space required due to the three sensors, space which is often not available.
The object of this invention is to configure a circuit of the described type such that the monitoring meets especially high safety requirements and can also be used even when the installation space is small.
The aforementioned object is achieved first of all and essentially by each monitoring and detection device having several different influence areas and several signal outputs. Here, within the framework of the invention the influence area is defined as that three-dimensional area at a distance to the monitoring and detection device within which the presence or absence of a monitored article leads to a change of state in the monitoring and detection device. In a conventional proximity switch the influence area is the area over the active surface of the proximity switch in which the latter reacts to the approach of the vaporizing material, i.e. a conventional proximity switch has exactly one influence area.
Because as claimed in the invention each monitoring and detection device has several different influence areas, accurate and selective monitoring of the state of the system is possible. Thus it is possible to distinguish not only between a faulty and a faultless state, but in addition the deterioration of the faultless state can be recognized and thus by initiating the corresponding measures the occurrence of a faulty state can possibly be avoided. When the location of the cable of a cable railway or chairlift system is being monitored relative to the cable pulleys which guide the cable, the lateral slippage of the cable can be detected.
In one preferred embodiment of the invention the monitoring and detection devices have one control input and one control output, the control output of monitoring and detection device (nxe2x88x921) being connected to the control input of the monitoring and detection device n. Thus, on the one hand the series connection of the monitoring and detection devices which is necessary for safety reasons is implemented, on the other hand the voltage drops on the monitoring and detection devices are prevented from adding up. The control input of the first monitoring and detection device is connected to the control and evaluation unit and a clocked signal which is preferably cyclically reprogrammed is supplied to it by the control and evaluation unit.
According to another teaching of the invention, in the circuit as claimed in the invention the monitoring and detection devices can be interrogated not only with respect to their state, especially with respect to their operating state, but can also be addressed. This means that each individual monitoring and detection device is individualized by a certain address being assigned to it. For the interrogation of the state of a certain monitoring and detection device therefore the monitoring and detection device which has been individualized by its address is xe2x80x9coperatedxe2x80x9d and then its state, in a version as a switching device its operating state, is interrogated. Here the monitoring and detection devices and the control and evaluation unit form a ring with respect to the interrogation and addressing possibility via the corresponding connecting lines.
Advantageously the addresses and information are transmitted via the connecting lines only in one direction, i.e. opposite the transmission direction of the clocked signal supplied by the control and evaluation unit to the control input of the first monitoring and detection device. Thus, failure of one monitoring and detection device or breakage of a transmission cable can be detected.
According to one preferred embodiment of the invention, one of the influence areas can be divided into two component areas, the subdivision into the two component areas taking place perpendicularly to the division into influence areas. In this way, in addition to the lateral slippage of a cable of a cable railway or chairlift system relative to the cable pulleys which guide the cable, a change of the cable location perpendicular thereto can also be acquired. This change of the cable location can occur for example when the cable pulleys change their position by their loading or when wear of the running surfaces of the cable pulleys occurs.